A pressure reducing valve is an apparatus which performs a function for reducing pressure of a fluid in the process of transporting a fluid through a pipe. A conventional pressure reducing valve has a passage way which is formed between an orifice, which is formed in a valve body for fluid passing, and a disk, of which a side faces to the orifice, disposed in a valve body, and adjusts opening rate of the passage way by controlling distance between the orifice and the disk, whereby pressure reducing function as well as adjustment of flow rate can be provided.
FIG. 1 is a longitudinally sectional view illustrating a conventional pressure reducing valve. A disk 12 moves by driving force generated by elastic force of a spring 16 which is coupled with the disk 12 through a driving shaft 14. The elastic force of the spring 10 is adjusted by a diaphragm 18 which is deformed by a pressure difference between an inlet side and an outlet side of an orifice for fluid flow. That is, the spring 16 serves as a direct power source of an operation for providing a pressure reducing function in the pressure reducing valve 10, and the diaphragm 18 serves to provide a function for adjusting opening rate of the passage way between the orifice and the disk.
However, when the conventional pressure reducing valve 10 is used for a long time, foreign materials mostly contained in a fluid can be accumulated in a space which accommodates the diaphragm 18. In this case, deformation of the diaphragm 18 cannot be properly induced, whereby the pressure reducing accuracy is deteriorated.
Also, it is important that the conventional automatic reducing valve must be able to always give a normal performance with which a reduced pressure can be still maintained at a pre-established level even in case that no fluid flows out of an outlet and thus the orifice is completely closed by the disk However, even though the orifice retains a completely closed state, a minute quantity of fluid leaking toward to an outlet through a minute crack to be formed at the passage way between the orifice and the disk causes a pressure in an outlet to gradually exceed the pre-established pressure and be finally equal to an inlet pressure. The minute crack can be formed due to a limited spring force to be applied to disk and/or a foreign materials settled on the surface of the disk which faces the orifice.
And particularly, in a fixed size of automatic pressure reducing valve no matter how largely an opening of the passage way between the orifice and the disk is opened, flow rate of a fluid to be passable through the orifice is limited at a constant pressure difference between the inlet and the outlet since an automatic pressure reducing valve with a fixed size has a fixed size of orifice in itself.
And also, the conventional pressure reducing valve 10 usually has not a structure with which an element functioning to detect an occurrence of flow is integrated.